Method for oriented emplacement of well casing to achieve directional drilling

ABSTRACT

The invention relates to a method and apparatus for the emplacement of an oriented conductor casing at a desired angle preliminary to slant drilling of a well in the substratum of an offshore well site. The method provides for the initial lowering of a well casing into the substratum. Thereafter the casing is forcefully urged downwardly whereby to bend and assume a curvature in a desired direction, as the casing advances along a preformed curved guide passage. The casing is progressively advanced until penetrating one or more competent subsurface formations.

United States Patent Inventor Johnnie J. Ziober Morgan City, La. Appl. No. 42,188 Filed June 1, 1970 Patented Oct. 5, 1971 Assignee Texaco Inc.

New York, N.Y.

METHOD FOR ORIENTED EMPLACEMENT OF WELL CASING TO ACHIEVE DIRECTIONAL DRILLING 7 Claims, 3 Drawing Figs.

[52] US. Cl 175/5, 175/61, 175/17] [51] Int. Cl E2lb 7/06, E2 lb 7/12 [50] Field of Search 175/5, 9, 61,79-81, 171, 257261 [56] References Cited UNITED STATES PATENTS 1,900,163 3/1933 Dana etal 175/61 X i/lwiecalvsoumria SIP/1m U C GOA/5041174750 SUP/m1 C.

2,565,794 8/1951 Young 175/61 2,873,092 2/1959 Dwyer 175/61 2,891,770 6/1959 Baueretal. l75/257X 3,004,612 10 1961 Kofahl 175/9x 3,115,755 12/1963 Siebenhausen 175/5x 3,426,844 2/1969 McDaniel 175/171X Primary Examinerlan A. Calvert Attorneys-Thomas H. Whaley and Carl G. Reis ABSTRACT: The invention relates to a method and apparatus for the emplacement of an oriented conductor casing at a desired angle preliminary to slant drilling of a well in the substratum of an offshore well site. The method provides for the initial lowering of a well casing into the substratum. Thereafter the casing is forcefully urged downwardly whereby to bend and assume a curvature in a desired direction, as the casing advances along a preformed curved guide passage. The casing is progressively advanced until penetrating one or more competent subsurface formations,

METHOD FOR ORIENTED EMPLACEMENT F WELL CASmG TO ACHIEVE DIRECTKONAL DRILLING BACKGROUND OF THE INVENTlON In the drilling of a well into the substratum of an offshore location, normally, the well is provided with a series of axially aligned casing which form a vertical, thin-walled passage. Thereafter, drill string carrying a drill bit and other ancillary fixtures is lowered through the passage and rotated to form the well itself.

The technique of slant or directional drilling of a well is often resorted to for a number of reasons. For one thing in the instance of offshore gas or oil fields, when the drilling is done from a stationary offshore platform, it is necessary to direct a number of wells radially from the platform to afford the most effective coverage of the area. This form of exploratory drilling is facilitated by initiating entrance of the drill string to the subsoil at an angle so that the latter enters the underwater substratum and immediately moves in the desired direction from the platform. Also, in the instance of a known subterranean pocket of gas and/or crude oil, it is desirable to tap the pocket with as many wells as is feasible. Consequently, a number of wells are directed at a downward angle from the platform into the area encompassing the pocket.

A further application of slant and/or directional drilling is found in the instance of a well that has become uncontrollably wild due to excessive pressure within a tapped pocket. In such an instance, rather than attempting to control the well through its own surface opening, slant drilling is resorted to whereby to afiord a safety valve for the pressure buildup by tapping into the field or gas pocket at an angle from the original well.

Various techniques for slant or directional drilling have been developed by the industry. One accepted method of directing a well along a predetermined or desired direction is by the use of special tool bits together with accessory equipment used with said bits. The direction which the bit assumes can also be, and is frequently altered by control of the downward pressure exerted on the bit by the string. This is achieved by manipulation of the supporting device within the derrick. Toward facilitating the slant or angle drilling of a well, the latter can also be commenced through a guide tube or similar member extending at an angle from the upper deck or platform, to the ocean floor. Thereafter the drilling string and tool bit are passed through the guide tube and can commence their passage into the substratum at the angle of the guide tube.

Where however, the substratum at the drilling site is of such a yieldable consistency as to prohibit the compatible drilling of a hole immediately into the ocean floor, the guide tube system is of course obviated. For example, in the instance of a floor comprised of an unconsolidated consistency such as a deltaic substratum, the consistency of the ocean floor renders it impossible to commence a well therethrough. Were such an attempt to be made, the walls of the formed well immediately collapse. Further, where the substratum is relatively unconsolidated, a tool entering at a predetermined angle would tend to gravitate toward a vertical disposition due to the weight of the drill string and collar, and inability of the substratum to maintain the string in a desired nonvertical direction.

It is therefore one of the objects of the present invention to provide a method for forming a subterranean well at an offshore location through a relatively unconsolidated substratum. A further object is to provide a drilling method for use in an offshore location characterized by a generally deltaic consistency beneath the ocean floor. A still further object is to facilitate the drilling of a slant or directionally controlled hole into an unconsolidated substratum at an offshore site by the use of standard, vertically oriented drilling equipment normally provided on drilling barges and rigs.

DESCRlPTlON OF THE DRAWINGS HO. 1 illustrates in a partially diagrammatic view, the present method of providing a slant drilled well from a stationary platform embedded at the floor of a body of water.

FIG. 2 is a segmentary view on an enlarged scale illustrating the lower end of a partially embedded well casing together with the drill string forming a guide hole in advance of the casing.

FIG. 3 is a cross-sectional view taken along line 3-3 in F K].

The invention, in brief provides a method and apparatus to facilitate the slant or directional drilling of an offshore well in a substratum, when the upper portion of the latter is characterized by a basically unconsolidated consistency. The method provides that initially, an elongated well casing be supportably lowered at a substantially vertical attitude into the substratum until the forward end transverses the unconsolidated or incompetent portion and enters a more consolidated strata. In such position, the suspended casing will be essentially supported at the upper end by the derrick, with the lower end embedded into a competent strata.

Thereafter, a guide passage is formed in the competent strata in advance of the casing lower end, into which guide passage the casing is forcefully urged. As a result, the casing walls are strained to adapt to the curvature of the passage walls. By forming the guide passage walls with a desired degree of curvature toward achieving an ultimate direction in the well, the casing will eventually be oriented at an angle deviated from the vertical, whereby to guide the drill string in a desired direction.

Because of the close similarity of parts in FIGS. 1 and 2, identical numerals are used in each FIG. to identify corresponding elements. Referring now to the drawings, FIGS. 1 and 2 illustrate in general an offshore well 10 being formed in a partially deltaic substratum. The latter is characterized by a generally unconsolidated or incompetent strata U disposed immediately beneath the surface of the ocean floor. in the instance of an area such as the Gulf of Mexico, this upper strata can be present up to several hundred feet of depth.

It is appreciated, that different offshore locations, even though sharing the common train of being incompetent, nonetheless bear similar subsoil profiles. An exemplary profile would consist of a series of horizontal layers made up of diverse soil compositions. These layers or strata can consist of varying gradations and proportions of sand, clay and other materials, In the aggregate, however, for several hundred feet of depth the layers will be incompetent to support a desired length of steel-walled casing.

Beneath this incompetent strata however, a layer C will be reached comprised of stiffer clay or the like, which substratum is capable of supporting a well casing merely by contact with the outer walls of the latter.

In the present arrangement, well 10 is drilled from a fixedly positioned marine platform 11 comprising a plurality of upstanding legs 12 and 13. The upper ends of the respective legs terminate above the water's surface and support a work deck 14. Following normal practice, deck 14 is movably or fixedly spaced a sufficient distance beyond the water's surface to protect equipment from undue exposure to wind and water.

Deck 14 is shown carrying the usual equipment ancillary to a well drilling operation. This includes a derrick 16 comprising an open steel structure having crown block 17 together with the necessary rigging for suspending a drill string 18 as the latter is lowered into well 10. Deck 14 further carries a draw works 19 which is connected to a rotary table 21, operably supported at the deck level whereby the drill string 18 can be rotated.

Platform ll is anchored at a predetermined offshore well site by piles 22 which are driven through the respective legs 12 and i3 and into the substratum. Normally, these piles are set sufficiently deep to afford the platform the degree of stability necessary to withstand adverse weather conditions while remaining in place at the well site. In accordance with present practice, the more incompetent or unconsolidated the consistency of the substratum, the greater will be the number of piles 22 required to satisfactorily and supportably anchor the platform.

In the present illustration, the depth of the water at the well site can lie within the limits of a minimal 25-foot depth, up to several hundred feet. The substratum U layer immediately underlying the water, as herein mentioned consists of a relatively unconsolidated material formed of mud and related compositions. Such substratum possesses minimal ability to maintain a heavy casing or other smooth walled body merely by a friction hold with the surface of the body. Experience has shown for example that relatively long casing strings have been lost in the Gulf of Mexico merely by sinking into the substratum due to their weight and to the inability of the latter to stabilize the casing.

Well casing 23, normally making up the outer wall of the well upper end, is formed of welded lengths of a heavy walled, steel cylindrical tubing. As the casing is progressively lowered into the substratum, incremental shorter casing lengths are welded to the upper end to provide a continuous open passage to 36 inches in diameter.

Under normal circumstances, after the outer well casing 23 is embedded into the substratum, a series of decreasingly smaller diameter diameter are loweredconcentrically trough said outer casing 23. Each successive casing section is fastened and cemented in place to form an elongated, gradually decreasing diameter passage. The latter then serves to guide the rotating, downwardly descending drill string 18 into the substratum, and to conduct drilling mud upward.

As shown in FIGS. 1 and 2, casing 23 is disposed at its upper end in a substantially vertical disposition with respect to the waters surface. This results since the steel casing is of sufficient bulk to embed itself by virtue of its own weight, through the water and the upper underconsolidated substratum U.

Physically, casing 23 is lowered progressively through the water. As the casing upper end is tightly clamped, incremental casing lengths are welded to the upper end at the deck. If necessary however, the casing is driven from the waters surface by a pile driver or similar apparatus carried on the platform or on an adjacently positioned barge. Further, where the substratum is relatively soft, the jetting process can be utilized whereby a downward passage is jetted vertically through the substratum thereby to facilitate embedment.

Again referring to FIGS. 1 and 2, casing 23 is downwardly urged to assume a gradual curvature from a depth beyond the strata interface and shortly after entering the consolidated substratum C. The curvature is maintained to the casing lower end until the latter reaches a desired depth. The casing at this point is oriented to facilitate drilling out in a particular direction.

As shown in FIG. 3, casing 23 lower end is comprised of a cylindrical member having a leading edge 24, and of sufficient wall thickness to lead the casing through a preformed guide passage 27. A portion of the periphery of casing 23 lower section can be provided with an outwardly protruding shoe section 26 arranged on the side in opposite to the direction in which the casing is to be deflected or deviated. Shoe section 26, as shown in FIG. 2, comprises in essence a tapered portion raised outwardly from a peripheral segment of the casing surface, to afford a backward drag on that side whereby the course of the casing will be deflected by the shoe 26.

Referring again to FIG. 2, casing 23 is advanced into the consolidated substratum by jetting a guide passage 27 ahead of the casing, and by then piling or otherwise forcing the casing through the subsequently formed guide passage. In the instance of consolidated substratum C, the means for forming passage 27 includes a jetting bit 28 carried at the drill string 18 lower end. A pressurized fluid such as water or drilling mud is pumped downwardly to, and out of the jetting bit, whereby to wash out a circular passage extending coaxially with the casing lower end. Jetting bit 28 is provided with a laterally directed jet to urge the bit in a desired direction. The working pressure of fluid emitted from the bit can of course be varied in accordance with the substratum to most effectively achieve a desired guide passage curvature.

In the normal operation of a jetting bit, the drill string and bit are lowered to the bottom of a hole to be drilled. The bit is so connected that only one or more jets remain unplugged as to urge the bit in a lateral direction. Without rotating the string, jetting fluid is pumped to the bit and discharged through said one or more open jets into the surrounding substratum. The pressurized liquid jetstreams loosen and erode the soil, to form a laterally exposed cavity. The bit is then advanced, the liquid pumping discontinued, and the drill string lower end follows the bit which gravitates toward a deviated course in the direction of the lateral cavity. The sequence of steps of jetting and drilling are thereafter continued to the desired depth.

In the present method, and as shown in the figures, casing 23 is first lowered vertically into the substratum a predetermined distance. This distance is such that the casing lower end will lie within the lower, more consolidated stratum denoted C. The casing can be further advanced into the consolidated substratum as shown in FIG. I, or as shown in FIG. 2 the procedure for altering the casings direction can be commended immediately upon entering the consolidated layer.

As jetting bit 28 is lowered past the casing 23 lower end to form guide passage 27, displaced material such as clay, sand, etc. from the passage is washed upwardly through the casing and disposed of. After guide passage 27 has been progresed a desired distance, bit 28 is withdrawn. Casing 23 is then urged into the guide passage by hammering or driving from above, or by otherwise applying a downward force against the casing. As the lower end of the latter advances into the passage, the walls of the casing will be forcibly strained to assume a curvature in conformance with that of said guide passage.

The sequential operations of embedding casing 23 into passage 27, as well as the predrilling of the passage, are repeated for short incremental lengths until the casing lower end is oriented at a predetermined depth and direction. Thereafter a hole is drilled and smaller diameter casing is inserted and cemented. The latter casing may be sufficiently small to enter the well bore without the necessity for driving.

With the well casing 23 set to its desired deviation and the smaller casing set in place, drill string 18 can be inserted, having a drill bit or a jetting head 28 at the lower end thereof. The well may now be further advanced in the usual manner by drilling or jetting as herein noted. As previously mentioned the direction at which the bit at this stage of the operation will advance to the substratum is dependent at least in part on the type of bit used as well as on the pressure applied to the drilling bit. Thus, any further angle of deviation or direction at which the drill bit progresses can be readily controlled from the waters surface.

Obviously many modifications and variations of the invention, as hereinafter set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. Method for the directional drilling of a subterranean well at an offshore location having a substratum characterized by an underconsolidated consistency at the ocean floor and a competent layer beneath said underconsolidated layer, which method includes the steps of;

a. embedding a cylindrical well easing into the substratum at a substantially vertical disposition and to a sufficient depth whereby the casing lower end is disposed in said competent layer,

b. forming a guide passage as a continuation of said casing, said guide passage being deviated to assume a gradual curvature an incremental degree from the axis of direction of said casing, and

c. advancing said casing into said guide passage whereby to bend said casing walls in conformance with the curvature of said guide passage, and

d. sequentially repeating said embedding, forming and casing advancing steps until said casing is aligned in a desired direction.

2. In the method as defined in claim 1 wherein said guide passage is formed with a cross-sectional area substantially equivalent to the cross section of said well casing.

3. In the method as defined in claim 1 wherein said well casing is advanced into said guide passage by being downwardly 5 driven from above the waters surface.

4. In the method as defined in claim 1 wherein said guide passage is formed by the displacement of substratum material and removal thereof upwardly through the guide passage.

5. In the method as defined in claim 1 wherein said guide 

1. Method for the directional drilling of a subterranean well at an offshore location having a substratum characterized by an underconsolidated consistency at the ocean floor and a competent layer beneath said underconsolidated layer, which method includes the steps of; a. embedding a cylindrical well casing into the substratum at a substantially vertical disposition and to a sufficient depth whereby the casing lower end is disposed in said competent layer, b. forming a guide passage as a continuation of said casing, said guide passage being deviated to assume a gradual curvature an incremental degree from the axis of direction of said casing, and c. advancing said casing into said guide passage whereby to bend said casing walls in conformance with the curvature of said guide passage, and d. sequentially repeating said embedding, forming and casing advancing steps until said casing is aligned in a desired direction.
 2. In the method as defined in claim 1 wherein said guide passage is formed with a cross-sectional area substantially equivalent to the cross section of said well casing.
 3. In the method as defined in claim 1 wherein said well casing is advanced into said guide passage by being downwardly driven from above the water''s surface.
 4. In the method as defined in claim 1 wherein said guide passage is formed by the displacement of substratum material and removal thereof upwardly through the guide passage.
 5. In the method as defined in claim 1 wherein said guide passage is formed by displacing material through hydraulic jetting with a high-pressure fluid stream.
 6. In the method as defined in claim 1 wherein said guide passage is formed by rotational drilling and removal of material from the formed passage.
 7. In the method as defined in claim 1 including the step of adding incremental lengths of said casing to the upper end thereof as the lower end is advanced into said guide passage. 